I'd highly recommend GLA. It's good stuff. I just now ran my CO2 tank bone dry yesterday, so 5lbs lasted about 2 months I guess. With my lighting I figure that's probably about right. I hadn't been keeping up with it, then I looked under yesterday to get some ferts out and noticed I had no bubbles rolling, hehe.
I'm also not using the Rex Grigg style reactor. I went with the house filter style one. I need to get some pictures of it as I don't think my thread is updated with all that.